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Deep understanding of SCTP security: from four-way handshake to defense against SYN attacks

introduction

In the world of network communication, security and reliability are crucial. Traditional TCP (Transmission Control Protocol) uses a three-way handshake when establishing a connection, but this mechanism has some security vulnerabilities, such as SYN attacks. SCTP (Stream Control Transmission Protocol), as an emerging transport layer protocol, effectively improves security by introducing a four-way handshake mechanism. This article will summarize the security advantages of SCTP in detail, compare it with TCP's three-way handshake mechanism, and explore the principles of SYN attacks and their defense strategies.

TCP three-way handshake and SYN attack

Three-way handshake mechanism

The establishment of a TCP connection relies on a well-known three-way handshake process:

1. Client sends SYN A: The client sends a synchronous request to the server, indicating that the client wants to establish a connection.
2. Server returns SYN B, ACK A 1: After receiving the request, the server caches the request and sends a synchronous response and confirmation to the client.
3. Client sends ACK B 1: After the client receives the response from the server, it sends a confirmation message to the server to complete the connection establishment.

How SYN attacks work

SYN attack exploits a weakness in the TCP three-way handshake process. The attacker sends a large number of SYN requests to the server, but does not complete the last step of the handshake. At this time, the server will maintain a large number of clients in the SYN-RECV state, thereby exhausting server resources. When there is a new SYN request, it will be discarded, affecting normal service.

SCTP's four-way handshake and security improvement

Four-way handshake mechanism

SCTP improves the security of connection establishment by introducing a fourth handshake:

1. The client sends INIT: The client sends an initialization request to the server.
2. The server returns an INIT ACK: After receiving the initialization request, the server returns a confirmation.
3. The server sends a COOKIE ECHO: The server sends a COOKIE to the client, requiring the client to carry the COOKIE in the next request.
4. The client sends a COOKIE ACK with the COOKIE: After the client receives the COOKIE, it returns it to the server in the request. The server establishes a connection after verification.

The role of cookies

The cookie mechanism in SCTP is the key to defending against SYN attacks. When the server receives a connection request, it does not immediately allocate memory resources, but generates a cookie and sends it to the client. The client carries this cookie in the next request, and the server verifies the cookie to confirm the identity of the client and the legitimacy of the request, thereby avoiding invalid allocation of resources.

in conclusion

By comparing the connection establishment process of TCP and SCTP, we can see that SCTP significantly improves security through the four-way handshake and COOKIE mechanism. This mechanism not only avoids SYN attacks, but also reduces the waste of server resources and improves the reliability of network communications. With the development of network technology, these advantages of SCTP may make it a more popular choice than TCP in some scenarios.